There have hitherto been reported a number of chemical vapor deposition (CVD) methods for the preparation of an aluminum oxide film. These methods are well summarized in recent review by E. Fredriksson et al., "Chemical Vapour Deposition of Aluminum Oxides from Various Gas Mixture," and J. Chemical Vapor Deposition, 1, 333-417 (1993) as well as in Korean translation of "CVD Handbook" pp 665-689 (Bando Publishing Co., Seoul, Korea, 1993). Aluminum trichloride and triisopropoxide have been most commonly used as aluminum sources in the CVD of an aluminum oxide film due to their low cost and ready availability. These conventional aluminum sources have low vapor pressures and are usually heated to higher than 100.degree. C. to generate a vapor stream to be used in a CVD process.
Further, trialkylaluminums have been used in the CVD of an aluminum oxide film, which are liquid at room temperature and have relatively high vapor pressure. However, such trialkylaluminums do not contain oxygen atoms, thus the use of an oxygen source such as O.sub.2 or N.sub.2 O is essential for the formation of an aluminum oxide film. Also trialkylaluminums are pyrophoric when exposed to air. U.S. Pat. No. 4,675,089 discloses a plasma-assisted CVD method of depositing an amorphous thin film of aluminum oxide using a trialkylaluminum vapor and carbon dioxide. However, this method requires expensive equipments to produce plasma and have lower throughput compared to a thermal CVD method, thus less suitable for use in a large-scale application.